1. Field of the Invention
The invention relates to a multilayered film with a polymer outer layer, a polymer connecting layer, and a heat-sealable polymer inner layer, to methods for producing it, and to its use.
2. Background Information
Such multilayered films or films, which are preferably heat-sealable, have long been used to produce liquid-tight and in particular water-vapor-proof bags. They are used particularly for bags used as primary packages for medical fluids and solutions. They can also be used as drainage bags. It is then usually sufficient if they are liquid-tight.
In special cases, especially whenever they are used for primary packaging for oxygen-sensitive materials, a suitable gas barrier property may also be desired. This is the case for instance when they are used to package amino acid solutions, or whenever the entry or release of CO.sub.2, for instance, may cause an undesired change in pH, or when the contents oxidize and thereby change if oxygen enters them.
For holding medical fluids and solutions, aside from the glass bottle, which is heavy and hard to handle, soft PVC bags are conventionally often used. They are satisfactory in terms of their flexibility and sealability, but they have the disadvantage that the plasticizers they contain readily diffuse, by migration within the PVC, into the interior of the bag, where they can cause utterly unwanted contamination of the contents. Especially in the case of solutions for IV or other infusions, it is extremely undesirable for these plasticizers to enter the patient's body along with the solution.
Another disadvantage of the known soft PVC bags is that because of the chlorine compounds and dioxins that are produced when they are incinerated, they present problems of waste disposal. It has already been proposed that instead of PVC (polyvinyl chloride), polyethylene bags be used. However, this material has the disadvantage that most types can be autoclaved (steamsterilized) at a maximum temperature of only 121.degree. C. The polyethylene alternatives also often lack the desired transparency and flexibility.
U.S. Pat. No. 4,778,679 to American National Can Company describes a multiple layer film which is also sterilizable and which has a combination of a connecting layer, primarily having HDPE, and a polypropylene mixture with a TPE as its outer layer. Combinations of polypropylene-based films with films having polyethylene-based polymers are employed, because the latter component avoids the brittleness and inflexibility of polypropylene while assuring that the film is free of halogen and is weldable. However, this known film was in need of improvement in terms of its external appearance (transparency).
German Patent Disclosure DE-A 44 10 876 has described a coextruded peelable multilayered film with a polypropylene-TPS mixture with an inner layer that can be heat-sealed at a temperature of 115 to 150.degree., a polypropylene homopolymer layer as the outer layer, and a polypropylene/VLDPE layer as the connecting layer. However, this known multilayered film is in need of improvement, both in terms of its transparency and flexibility and in terms of the adhesion of the layers forming the multilayered film to one another, as can already be inferred from the fact that it is a peelable film, i.e. one whose layers can be separated from one another.
European Patent EP 0 437 846 (to Idemitsu) also describes a peelable multilayered film product based on polystyrene, in which layers containing polypropylene are produced jointly with layers containing polystyrene, in the form of easily separable--that is, peelable--layers.
It can thus be inferred that in many known multilayered films with a high proportion of polypropylene, joining the layers to one another, which is essential for both the strength and appearance of the film composite, is problematic.
The basic demands made of multilayered films for use in packaging aqueous solutions, especially solutions for IV infusion and the like, are thus that they have
high flexibility PA1 very good transparency PA1 low water vapor permeability; and are PA1 physiologically safe, with mechanical stability; PA1 sealable with permanently heated tools or be pulse-weldable PA1 autoclavable, even above 121.degree. C., and PA1 that for particular foods or medical fluids and solutions, an additional barrier effect against oxygen and/or carbon dioxide may also be present. PA1 Wine, freeze-dried coffee extract and jam. PA1 Saline solutions, blood, blood substitute solutions, dialysis solutions, and amino acid solutions--but other paste-like or liquid or dry materials may also be packaged, especially those that might have to be sterilized or are placed in the packages while hot.